Transient Chirality in Chemistry and Biology: Capturing the Structural Evolution of Molecules in Solution

  • Datum: 27.11.2019
  • Uhrzeit: 11:00
  • Vortragender: Malte Oppermann
  • Ecole Polytechnique Fédérale de Lausanne & LACUS, Lausanne, Switzerland
  • Ort: CFEL (Bldg. 99)
  • Raum: Seminar Room IV, O1.111
  • Gastgeber: Andrea Cavalleri / Angel Rubio
Most biological functions and many chemical processes are driven by chiral nanoscale molecular machines in solution, whose structures evolve on multiple time and length scales: from the ultrafast rotations of photo-driven synthetic molecular motors to the global conformational changes of proteins on the microsecond time scale. Yet capturing the associated conformational transitions in real-time continues to be a formidable experimental challenge, as prominent established methods come with their own limitations: solution nuclear magnetic resonance is limited to millisecond real-time resolution, whilst solution X-Ray scattering requires large-scale X-Ray facilities. A promising laboratory-based alternative is circular dichroism (CD), the absorption difference of left- and right-handed circularly polarized light, which is sensitive to the chiral geometrical arrangement of light-absorbing chemical groups within a molecular system. Steady-state CD is already a well-established tool in the far and middle ultraviolet (UV) < 300 nm, where equilibrium structures of proteins, DNA and functional chiral organic complexes are routinely characterized. However, pushing this technique into the time-domain has remained a challenge for over three decades, with only few isolated reports with sub-nanosecond resolution [1]. In this talk, I will present a technological breakthrough with the first time-resolved CD (TRCD) spectrometer that combines highly sensitive broadband UV-detection (250-370 nm) with pulsed laser sources and sub-picosecond time-resolution [2]. With this instrument, it is now possible to extract broadband CD spectra of photo-excited molecular states and follow their transient chirality changes with femtosecond resolution. This is opening a new avenue for capturing solution-phase structural dynamics in chemical and biological systems that I will illustrate with two examples: the coupling of electronic and structural dynamics in a chiral supramolecular metal-complex [3], and the application of a site-specific CD-label to track conformational changes of the peptide backbone [4]. On this basis I will present future developments that will establish TRCD as a complementary method for research in protein dynamics and chiral photochemistry, where the chirality of excited electronic states is the key design feature of chiral organic light-emitting diode materials and unidirectional molecular motors, for example.

[1] J. Meyer-Ilse et al., Laser Photon. Rev. 7, 495 (2013)
[2] M. Oppermann et al., Optica 6, 56 (2019)
[3] J. Lacour et al., Angew. Chem. Int. Ed. 37, 2379 (1998)
[4] M. Oppermann & J. Spekowius et al., J. Phys. Chem. Lett. 10, 2700 (2019)

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